Visible light absorbing colorants (e.g., dyes, in particular pigments) have been incorporated into contact lenses to enable the consumer to easily locate the lens in a clear solution within a lens storage, disinfecting or cleaning container. Dyeing a lens for this purpose is termed “visibility tinting” the lens.
Visibility tinting may be accomplished by applying a colorant to a portion of the surface, or by applying a colorant to the full front surface of the lens. Alternatively, a colorant may be incorporated into the full body of the polymer matrix of the lens. There have been a number of patents and published patent applications relating to tinting contact lenses. However, the known processes are not yet totally satisfactory. For instance, a pigment dispersion, especially a lens-forming formulation with pigments having submicron particle size may not be stable over an extended long period of time, for example, at least four days or longer. Consequently, the production efficiency and/or the quality of the products obtained can be adversely affected by such problem.
Therefore, there is still a need for a method of making a visibility tinted, i.e., full-body tinted, contact lens with an improved efficiency by, for example, providing a lens-forming formulation including pigment particles with an increased stability.